Astroorientation inLethrus (Coleoptera, Scarabaeidae)

SUMMARYThe present study first examined whether ruin lizards Podarcis sicula are able to orientate using the e-vector direction of polarized light. Ruin lizards were trained and tested indoors, inside a hexagonal Morris water maze, positioned under an artificial light source producing plane polarized light with a single e-vector, which provided an axial cue. Lizards were subjected to axial training by positioning two identical goals in contact with the centre of two opposite side walls of the Morris water maze. Goals were invisible because they were placed just beneath the water surface, and water was rendered opaque. The results showed that the directional choices of lizards meeting learning criteria were bimodally distributed along the training axis, and that after 90deg rotation of the e-vector direction of polarized light the lizards directional choices rotated correspondingly, producing a bimodal distribution which was perpendicular to the training axis. The present results confirm in ruin lizards results previously obtained in other lizard species showing that these reptiles can use the e-vector direction of polarized light in the form of a sky polarization compass. The second step of the study aimed at answering the still open question of whether functioning of a sky polarization compass would be mediated by the lizard parietal eye. To test this, ruin lizards meeting learning criteria were tested inside the Morris water maze under polarized light after their parietal eyes were painted black. Lizards with black-painted parietal eyes were completely disoriented. Thus, the present data show for the first time that the parietal eye plays a central role in mediating the functioning of a putative sky polarization compass of lizards.

Section: Discussionmentioning

confidence: 56%

A sky polarization compass in lizards: the central role of the parietal eye

Beltrami

Bertolucci

Parretta

et al. 2010

“…Once the beetle has reached the end of the barrier, it can again set out parallel to its previous course (Fig.·6A). The same manipulation on a homing animal will result in a new course to compensate for the sideways movement caused by the barrier (Fig.·6B; Frantsevich et al, 1977;Schmidt et al, 1992). The direction of this new course is obtained by path integration (Müller and Wehner, 1988).…”

Section: Discussionmentioning

confidence: 99%

Twilight orientation to polarised light in the crepuscular dung beetleScarabaeus zambesianus

Dacke

Scholtz

2003

109

The polarisation pattern of skylight offers many arthropods a reference for visual compass orientation. The dung beetle Scarabaeus zambesianus starts foraging at around sunset. After locating a source of fresh droppings, it forms a ball of dung and rolls it off at high speed to escape competition at and around the dung pile. Using behavioural experiments in the field and in the laboratory, we show that the beetle is able to roll along a straight path by using the polarised light pattern of evening skylight. The receptors used to detect this skylight cue can be found in the ommatidia of the dorsal rim area of the eye, whose structures differ from the regular ommatidia in the rest of the eye. The dorsal rim ommatidia are characterised by rhabdoms with microvilli oriented at only two orthogonal orientations. Together with the finding that the receptors do not twist along the length of the rhabdom, this indicates that the photoreceptors of the dorsal rim area are polarisation sensitive. Large rhabdoms, a reflecting tracheal sheath and a lack of screening pigments make this area of the eye well adapted for polarised light detection at low light levels. The fan-shaped arrangement of receptors over the dorsal rim area was previously believed to be an adaptation to polarised light analysis, but here we argue that it is simply a consequence of the way that the eye is built.

“…A similar situation was found in field crickets (Gryllus campestris) and desert locusts (Schistocerca gregaria), in which the sky polarization compass mainly uses linear polarization in the blue ( max 433 and 450nm, respectively) and not in the UV (Herzmann and Labhart, 1989;Eggers and Gewecke, 1993). In several other species, however, such as the honey bee A. mellifera, the desert ant C. bicolor and the scarab beetles Lethrus spp., the sky polarization compass does not work in the absence of linear polarization in the UV (von Helversen and Edrich, 1974;Edrich and von Helversen, 1987;Duelli and Wehner, 1973;Frantsevich et al, 1977). In an attempt to explain that discrepancy, Zufall et al (Zufall et al, 1989) proposed that highly polarization-sensitive blue receptors may be a common adaptation for insects active not only during the day, but also during crepuscular periods and at night, such as field crickets, as opposed to exclusively day-active insects -honeybees, desert ants and flies -which predominantly use UV receptors to detect skylight polarization.…”

Section: Discussionmentioning

confidence: 99%

“…In the ruin lizard, it was shown for the first time that the parietal eye, a component of the reptile pineal complex, plays a central role in the functioning of a sky polarization compass (Beltrami et al, 2010). Species in which orientation behaviour was systematically examined under selected wavelengths of polarized light, such as the honey bee A. mellifera, the desert ant Cataglyphis bicolor and the scarab beetles Lethrus spp., were shown to use a sky polarization compass only in presence of light in the ultraviolet (UV) range (von Helversen and Edrich, 1974;Duelli and Wehner, 1973;Edrich and von Helversen, 1987;Frantsevich et al, 1977). In contrast, in ruin lizards a sky polarization compass was demonstrated to work in the absence of UV light (Beltrami et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

The lizard celestial compass detects linearly polarized light in the blue

Beltrami

Parretta

Petrucci

et al. 2012

SUMMARYThe present study first examined whether ruin lizards, Podarcis sicula, are able to orientate using plane-polarized light produced by an LCD screen. Ruin lizards were trained and tested indoors, inside a hexagonal Morris water maze positioned under an LCD screen producing white polarized light with a single E-vector, which provided an axial cue. White polarized light did not include wavelengths in the UV. Lizards orientated correctly either when tested with E-vector parallel to the training axis or after 90deg rotation of the E-vector direction, thus validating the apparatus. Further experiments examined whether there is a preferential region of the light spectrum to perceive the E-vector direction of polarized light. For this purpose, lizards reaching learning criteria under white polarized light were subdivided into four experimental groups. Each group was tested for orientation under a different spectrum of plane-polarized light (red, green, cyan and blue) with equalized photon flux density. Lizards tested under blue polarized light orientated correctly, whereas lizards tested under red polarized light were completely disoriented. Green polarized light was barely discernible by lizards, and thus insufficient for a correct functioning of their compass. When exposed to cyan polarized light, lizard orientation performances were optimal, indistinguishable from lizards detecting blue polarized light. Overall, the present results demonstrate that perception of linear polarization in the blue is necessary -and sufficient -for a proper functioning of the sky polarization compass of ruin lizards. This may be adaptively important, as detection of polarized light in the blue improves functioning of the polarization compass under cloudy skies, i.e. when the alternative celestial compass based on detection of the sun disk is rendered useless because the sun is obscured by clouds. Supplementary material available online at